1. Field of the Invention
The present invention relates generally to a reaming device and, more particularly, to an expandable reaming device that may be used for reaming an acetabulum in preparation for implanting a prosthetic component, such as an acetabular cup or socket during a hip arthroplasty.
2. Related Art
The hip joint is a ball-and-socket joint formed by the articulation of the rounded, convex surface of the head of the femur with the cuplike acetabulum on the pelvis. In a healthy hip joint, the head of the femur and the acetabulum are lined by surface cartilage; the entire joint is surrounded by a capsule which has a thin lining of synovial cells that produce a thin layer of lubrication film called synovial fluid. The synovial fluid, together with the cartilage, acts as a shock absorber and allows the joint to move. If the surface cartilage is badly damaged, or if the joint surfaces are not aligned properly, then the cartilage will wear out, and as a result, the bone under the cartilage layer is exposed. The exposed bone starts to rub against each other and the process of osteoarthritis is established.
Osteoarthritis is the result of mechanical wear and tear on a joint, in this case, the hip joint. The main indication is a loss of surface cartilage due to the bone rubbing on bone. The formation of bone spurs, called osteophytes and cysts around the joint is another indication of osteoarthritis. The body tries to relieve the pain from the rubbing of the bone by increasing the amount of fluid in the joint. In an arthritic hip, the cartilage lining is thinner than normal or completely absent; the capsule of the arthritic hip is swollen; the joint space is narrowed and irregular in outline; and/or excessive osteophytes can build up around the edges of the joint. The combination of these factors cause pain and will eventually result in the loss of motion of the hip.
Hip arthroplasty is a surgery performed to replace all or part of a joint, deteriorated from osteoarthritis, with an artificial device in order to restore joint movement. There are different types of hip arthroplasty. If a hemi-arthroplasty is performed, either the femoral head or the acetabulum is replaced with a prosthetic device. In a total hip arthroplasty, both the femoral head and the acetabulum are replaced with prosthetic devices. Hip arthroplasty involves reforming the patient's natural acetabulum, so that a proper bearing surface for the ball of a femur is established in order to support the normal motion of the leg. The acetabulum needs to be reshaped so that it can properly receive a metallic or plastic artificial socket; typically osteophytes and other deteriorated and diseased bone are removed from within and around the acetabulum using a bone chisel, until healthy bone becomes visible. Typically, a reamer is used to accomplish this reshaping of the acetabulum, and reamer heads of increasingly larger size are required as bone is cut away and the socket is enlarged. Each time a larger reamer head is needed, the reaming system must be removed from the patient's acetabulum, the reamer head is removed from the drive shaft of the surgical drill, and the next larger reamer head is attached. This sequence may be repeated several times until the acetabulum is completely prepared to receive an acetabular prosthetic implant. The process of replacing reamer heads multiple times during a surgery is time consuming, inefficient, inconvenient, and may also lead to surgical errors in that the angle of acetabular penetration may not be accurately preserved during each reamer head substitution.
Standard hip arthroplasty is typically performed using a posterolateral or anterolateral approach, with an incision of 25-30 cm in length (see FIG. 1A). The approach provides substantial exposure, and complete and continuous observation, of the hip. With this large incision, it is unlikely that the reamer will be off axis. However, this exposure comes at the expense of trauma to the muscle and tendons and of considerable postoperative pain, requiring inpatient stay and delay of postoperative physical therapy.
Recently, minimally invasive (MIS) hip arthroplasty has been used as an alternative. MIS hip arthroplasty approaches include single-incision and 2-incision techniques, wherein each incision measures about 10 cm in length (see FIG. 1B). With the MIS techniques, a decrease in muscle and tendon trauma is achieved at the expense of not having complete and continuous observation of the hip. With a small incision, it is more difficult to place the acetabular reamer in direct alignment with the axis of the acetabulum. If the smaller incision is not exactly aligned with the acetabulum (see FIG. 2A), the reamer will be off axis relative to the axis of the acetabulum. If the reamer is off axis and the head of the reamer has hemispherical or less cutting capability (“180 degrees or less head”), it will be unable to cut a perfect hemisphere in the acetabular space (see FIG. 2B). A portion P of the acetabular space will be improperly reamed, or, more likely, not reamed at all. Therefore, the inventor believes that there is still a need for an acetabular reamer that is expandable to eliminate the need for multiple reamers and a reamer head that is greater than 180 degrees to allow the surgeon to cut a perfect hemisphere even when the reamer is off axis.
Issued patents relating to expandable acetabular reaming devices include the following:
Fishbein (U.S. Pat. No. 3,702,611) discloses an expanding reamer including a head with a convex end adapted to seat in a previously-prepared concavity in the central part of the acetabulum; the head pivotally mounts a set of expansive blades and is telescopically mounted on the end of a rotary drive shaft.
Temeles (U.S. Pat. No. 6,283,971) discloses an expandable acetabular reaming system having a plurality of blades that project or retract through a reamer head according to a desired reamer head size. The degree projection or retraction of the reaming blades is manually controlled by user actuation of an air bladder.